1. Field of the Invention
This invention relates to a silo type combustor for a gas turbine engine used to provide rotational power to an electrical generator, and specifically to a gas turbine engine with a silo combustor that operates at very reduced levels of nitric oxide (NOx) emissions.
2. Description of Related Art
In recent years, emissions regulations with the Federal Government has become of great concern to manufacturers and operators of gas turbine engines used to generate electricity, and, in particular, of pollutants produced by the gas turbine combustor. Of specific concern are nitric oxides (NOx) because of their large contribution to air pollution. Depending upon the gas turbine installation site, emission requirements vary, in terms of parts per million (ppm) of NOx that can be emitted each year. Therefore if a particular gas turbine engine is used very little in a year, a higher emissions combustor can be used. However if a gas turbine engine is run on a regular basis, a lower emission combustor system is required to meet emission regulations. In the past, NOx emissions have been reduced by the injection of water or steam in to the combustion process. Although this is an acceptable process, it has many disadvantages including system complexity, the cost of water treatment and increased heat rates. In order to meet pollution emission requirements without using one of the previously mentioned options, operators of gas turbines are required to upgrade older, higher pollutant emitting engines to include a combustion system that emits a lower level of NOx than their existing systems. Each engine manufacturer has taken steps to provide a combustion system capable of reducing NOx emissions to acceptable levels. Most common low emission combustors use natural gas instead of liquid fuel and have improved airflow, cooling, and mixing conditions.
Gas turbine engines have certain essential components such as a combustor, a compressor section, a turbine section and the power shaft. Gas turbine combustors vary in geometric configuration, fuel nozzle arrangement, fuel utilized and emission results. For example, one particular gas turbine engine utilizes a xe2x80x9csiloxe2x80x9d combustor which is stacked vertically above the engine centerline. Older, higher emitting combustor arrangements can use one liquid fuel nozzle for mixing liquid fuel and compressor discharge air. This combustor arrangement typically produces emissions in excess of new environmental regulations. The present invention provides an improved combustor system using the silo configuration to produce low emissions for a natural gas turbine engine. U.S. Pat. No. 4,292,801 describes a gas turbine engine that employs a horizontal combustor mounted in line with the turbine section and the compressor section.
The use of a silo combustor can result in a more compact turbine engine, saving space, and providing for operational improvements due to its mounting and location relative to the turbine and compressor sections of the engine. In addition the silo plenum allows for improved fuel/air mixture and a uniform pattern prior to the turbine section.
U.S. Pat. No. 5,611,197 issued to Bunker Mar. 18, 1997 shows a closed circuit air cooled turbine. Each combustor 20 is mounted offset from the power shaft such that the output of each of the combustors is directed to a small area of the turbine blades. A plurality of combustors are utilized, each having an output at a different area of the turbine blades. Utilizing the silo orientation of the present invention, a 360 degree output covering the entire turbine blade section can be achieved using a plurality of individual combustors as described further herein.
A gas turbine engine used for providing power to operate an electrical generator typically for a utility grid comprising a silo combustion system that includes a plurality of two-stage, two-mode combustors for producing low NOx emissions, a turbine system driven by the exhaust gases from said combustion system for providing rotational energy, and a compressor system providing compressed air to said combustion system, said turbine system including an output shaft used to drive a generator as well as the compressor system.
The turbine system and the compressor system are joined by the operating shaft mounted horizontally and linearly in the overall turbine engine housing.
The combustion system is mounted vertically between said turbine system and said compressor system and includes a combustion gas output channel that communicates directly with the turbine blades providing high velocity exhaust gases that are used to drive the turbine blades.
The vertically mounted combustion system includes a plurality of individual combustors mounted on a top cap through annular openings in the top cap of the combustion system. In the embodiment disclosed herein, a plurality of twelve individual combustors are mounted in a ring (annularly) around the combustion top cap.
Each combustor is comprised of a two-stage, two-mode combustor that includes six primary fuel nozzles and one secondary, centrally-located fuel nozzle to provide two-stage operation.
The exhaust gases from each combustor enters a common plenum chamber. The combusted gases under high pressure are directed through a transition channel into an annular chamber that is in 360 degree communication with the turbine blades. Thus the combustion gases which drive the turbine blades interact around a 360 degree area rather than having individual combustion gas feed chambers from each individual combustor as shown in the prior art. A common plenum chamber provides a more uniform exhaust pattern to the turbine, where as in prior art, individual exhaust ducts to sections of the turbine may differ in pressure, temperature and affect turbine performance.
The use of two-stage individual combustors results in very low NOx polluting emissions because of high efficiency of each combustor.
Each combustor also includes a venturi section within the combustion liner that utilizes an improved cooling air transfer system. This system cools the entire liner, including the venturi. While cooling the venturi, the air is preheated by radiation from the secondary combustion chamber, and is then directed into the upstream/premix combustion chamber for use in the combustion process. This additional air lowers the fuel/air ratio, which in turn lowers combustion flame temperature and emissions. The improved use of cooling air for a combustion liner for lowering emissions is disclosed in applicant""s current pending U.S. patent application Ser. No. 09/605,765 which is hereby incorporated by reference into this application. The use of the improved device described above in applicant""s patent application is used in all twelve combustors utilized in the present invention.
It is an object of this invention to provide an improved gas turbine engine used for generating electrical power that has low NOx pollutants and emissions while utilizing a combustion system that is vertically oriented and uses a common plenum exhaust gas chamber in fluid communication with the turbine blades.
It is another object of this invention to use a plurality of two-stage, two-mode combustors in a vertically oriented combustion system for use in a gas turbine engine to reduce NOx emissions while providing exhaust gases in a 360-degree fed chamber through the turbine blades.
Yet still another object of this invention is to provide an improved silo type combustor for a gas turbine engine that has a common plenum using a plurality of individual combustors of high efficiency.
But yet still another object of this invention is to provide a vertically oriented combustion chamber that includes two-stage, two-mode combustors with a vertically oriented combustion system to improve gas flow distribution throughout the combustion process.
In accordance with these and other objects which will become apparent hereinafter, the instant invention will now be described with particular reference to the accompanying drawings.